The donors were being "vilified and attacked" for giving money to political parties because of the Conservative's poor handling of the scandal.

They are increasingly concerned about their reputation after Peter Cruddas, the former party treasurer, was caught offering access to David Cameron for hundreds of thousands of pounds.

One donor said he was adopting a “hedgehog approach” and stopping giving altogether: “My cheque book has been put away – there is no possibility of privacy”.

Another told The Daily Telegraph that businessmen “should be praised, not vilified and attacked” for donating money to political parties.

The donor said: “I can’t stand Nick Clegg but he did say one sensible thing when he talked about how we should encourage people to give money to parties and they should be praised for it, not vilified and attacked.”

The donor complained that Mr Cruddas’ actions had made donating to political parties look “dirty” and questioned why he and other major donors were not “applauded” for giving money to political parties,.

The businessman added that when he gave the money he was “made out to be a horrible person – I thought ‘Oh God, this is my opinion, I support this party, I want them to be successful, why shouldn’t I be allowed to do that?’ In another country I would probably be applauded for it.”

The donor added that it was ridiculous to suggest that people who gave money to the Tories could influence policy given the Liberal Democrat ‘lock’ on the Coalition.

He said: “To think that any donor has any influence over this Govt is a joke, in fact if anything there is a huge frustration with what the Govt is doing as donors.”

Future party benefactors would be “nervous” about who is brought in to replace Lord Fink, the veteran treasurer who was brought in to replace Mr Cruddas.

Another donor said they “will be looking at the choice of the next treasurer after Stanley [Fink] very carefully”.

Talks are due to start in by the end of tomorrow [fri] on how to find a way out of the crisis over party funding, with the Conservatives and Labour still a long way apart.

Earlier this week Francis Maude, the Conservative Cabinet Office minister, renewed calls for Labour to agree on a cap of £50,000 on donations to parties.

But he insisted that this limit must apply not only to individuals and companies but also to unions. This meant that any deal was unlikely to be agreed by Labour, and showed how far the two sides have to go to get agreement.

Earlier this week Number 10 had been forced to admit that Mr Cameron had held a number of private dinners for donors in his private flat in Downing Street, and at Chequers, the Prime Minister’s official country residence.

The news came as Labour tried to keep up the pressure over the Cruddas affair, claiming that Mr Cameron could have broken the ministerial code, which states that government facilities should not be used for party activities.

In a letter to Sir Jeremy Heywood, Cabinet secretary, Shadow Cabinet minister Jon Trickett said that one of the meals broke the code because it took place in the Downing Street offices, and not in the flat above.

Mr Trickett also demanded an explanation over reports that Lord Feldman, the party chairman, was allowed a desk at Number 10.

An aide to Mr Cameron said: "We don't believe the code has been broken." He added Lord Feldman, an old friend of Mr Cameron, did not have a desk in Downing Street but attended meetings there.

He added that a “handful” of party workers did have desks in Downing Street, following a precedent set by other Prime Ministers.